1. Field of the Invention
The present invention relates to heat shield devices which are used in turbomachines, especially in gas turbines.
2. Description of the Related Art
The high cycle efficiencies of turbo- or hydrodynamic machines, especially gas turbines, which are now customary can only be achieved using high compression ratios of the working fluid in a compressor of the turbomachine. Air is generally used as the. working fluid here. High compression ratios or pressure ratios in a compressor lead in turn to the temperature of the flowing fluid at the compressor outlet rising as well. However, the temperatures of the working fluid resulting from the now customary compression of the fluid to about 30 bar or above are often above the maximum permissible material temperatures of the components of the turbomachine. Particularly in the compressor, the materials used hitherto have generally been materials with only a limited heat resistance. On the one hand, these materials with limited heat resistance are significantly cheaper than materials of higher heat resistance and moreover frequently have further advantages, such as good machineability or higher tensile strength. It is therefore desirable to continue manufacturing the components from these materials of lower heat resistance, particularly in the compressor zone. While, in the area of a rotor, the basic rotor element is protected from the working fluid by blade end elements of platform-like design, the basic rotor element is exposed directly to the working fluid, especially in the area of a stator constructed without a shroud ring. In order to prevent overheating of the basic rotor element, in particular, during the operation of the turbomachine, heat-accumulation segments were arranged here in the areas in which the basic rotor element is not protected from the working fluid by the blade end elements of the rotor blades (e.g. in DE 196 15 549). This arrangement comprises plate-shaped elements which are matched to the contour of the basic rotor element and can be secured on the basic rotor element by means of special anchoring devices. While the basic rotor element is produced from a simple ferritic material, the heat shield element is manufactured from a material which is highly heat resistant. However, the arrangement described in DE 196 15 549,especially the securing of the heat-accumulation segments, involves a very high outlay in terms of design and consequently is very expensive to produce. Moreover, this arrangement leads to a larger number of components of the turbomachine, giving rise in turn to higher costs, especially for assembly and maintenance. Another disadvantage of this arrangement is the increased risk that the rotor blades will scrape against the heat-accumulation segments. One reason for this increased risk is the difference in material properties, in particular different coefficients of thermal expansion and thermal conductivity of the guide vanes, the basic rotor element and the heat-accumulation segments, leading to thermal expansions which progress at different rates during the starting of the turbomachine or in the case of load changes of the turbomachine. Moreover, the components are subject to dimensional tolerances inherent in their manufacture. Owing to the increased number of components, it is easy for a situation to arise in which the gap between the guide vanes and the heat-accumulation segments is less than a nominal gap. This reduced dimensional accuracy of the gap can in turn lead to rubbing of the components in the event of mechanical or thermal expansion. Such rubbing leads at the very least to abrasion of the guide-vane tip and of the heat-accumulation segment, leading to enlargement of the gaps and consequently to a reduction in the efficiency of the turbomachine. However, rubbing of the guide vanes can also lead to damage of the guide vanes and even to the guide vanes breaking off.
It is therefore the object of the invention to provide a device with the aid of which a basic rotor element of a rotor can be protected from the high temperatures of the working fluid and the disadvantages of the prior art can be avoided in an advantageous manner. At the same time, it should, in particular, be possible to produce the devices according to the invention with a low outlay on manufacture and thus economically in comparison with the prior art.
In addition to the basic rotor element, also referred to as the rotor disk, a conventional rotor, in particular a rotor of a turbomachine, comprises a multiplicity of rotor blades which are arranged in at least one row on the circumference of the basic rotor element. There is furthermore generally a row of guide vanes in front of or behind the row of rotor blades. The paired arrangement of in each case one row of rotor blades and one row of guide vanes is referred to as a stage of a compressor or a turbine of a turbomachine. Compressors or turbines of turbomachines generally comprise a plurality of stages arranged one behind the other. In a first aspect of the invention, a heat shield element or a plurality of heat shield elements lined up on the circumference of the basic rotor element is arranged between the basic rotor element of a rotor and the rotor blades of at least one row of rotor blades. According to the invention, the heat shield element or the lined-up heat shield elements in each case extends or extend in the axial longitudinal direction; of the basic rotor element at least both over the area of the row of rotor blades and over the area of a row of guide vanes positioned in front of or behind the row of rotor blades. In this arrangement, the heat shield element or heat shield elements completely surrounds and covers or surround and cover the basic rotor element in the areas of the row of rotor blades and the row of guide vanes. Over the entire circumference of the basic rotor element, the working fluid thus does not come into direct contact with the basic rotor element. As a consequence also, heat is not transmitted directly from the working fluid to the basic rotor element. The working fluid is here not necessarily the main working fluid of the turbomachine but can also be some other hot fluid from which the basic rotor element is to be shielded. An intermediate gap, which is as continuous as possible and in which a fluid, generally air, is advantageously present, preferably remains between the basic rotor element and the respective heat shield element. In order to transmit heat from the working fluid to the basic rotor element, multiple heat transfer is consequently required at the respective boundary surfaces and also conduction of the heat in the heat shield element. In this arrangement, the multiple heat transfer at the boundary surfaces advantageously increases the insulating effect of each heat shield element in relation to the basic rotor element. It has been found that, with the arrangement according to the invention of one or more heat shield elements, a significantly lower temperature is established in the basis rotor element than without these heat shield elements. It is thus possible, in the case of an arrangement according to the invention of the heat shield elements, to produce the basic rotor element from a material of limited heat resistance, e.g. a ferritic material, while the heat shield elements are preferably produced from highly heat resistant material, which preferably furthermore has a low thermal conductivity. The heat shield elements according to the invention are preferably employed in a compressor of a turbomachine since here even a slight reduction in the temperature loading of the basic rotor element is often sufficient to allow the use of ferritic materials for the basic rotor element.
By virtue of the embodiment according to the invention of the rotor, the outlay on manufacture can be considerably reduced compared with the embodiments known from the prior art. The embodiment according to the invention can thus be produced at considerably lower cost than previous embodiments. Moreover, dimensional accuracy of the arrangement is easier to achieve by virtue of the smaller number of components. This increases both the operational reliability and the efficiency of the turbomachine. The increase in efficiency results from the fact that the gaps between the heat shield elements and the guide vanes can be made smaller.
In a preferred embodiment of the invention, the heat shield element or heat shield elements extends or extend over a plurality of rotor-blade rows arranged one behind the other and over the areas between the rows of rotor blades. The rows of guide vanes are generally arranged in the areas between the rows of rotor blades in the overall assembly of the turbomachine. It is thus advantageously possible to further reduce the number of components. The number of joints between the heat shield elements is furthermore reduced. Joints of this kind are unwanted because it is possible here for working fluid to flow into the joints and thus for direct contact to occur between the working fluid and the basic rotor element.
A second aspect of the invention relates to a rotor, in particular a rotor of a compressor of a turbomachine, which comprises a basic rotor element and a multiplicity of rotor blades, the rotor blades being arranged in a distributed manner in at least two rows on the circumference of the basic rotor element. An area for a row of guide vanes is provided between the rows of rotor blades. According to the invention, one or more heat shield elements lined up on the circumference of the rotor are arranged in such a way between the basic rotor element and the rotor blades of each row of rotor blades that, when assembled, the heat shield elements completely surround and cover the basic rotor element in the areas of the rows of rotor blades and the row of guide vanes. In this arrangement, the heat shield elements also extend into the area of the row of guide vanes. In this arrangement, it is advantageous if the heat shield elements each extend into the center of the area of the row of guide vanes. The mode of operation of the heat shield elements in accordance with the second aspect of the invention is fundamentally the same as the mode of operation of the heat shield elements, arranged in the rotor, in accordance with the first aspect of the invention. However, an embodiment in accordance with the second aspect of the invention offers the advantage that only rotor blades of one row of rotor blades or even each rotor blade itself is/are arranged on one heat shield element. The rotor blades of each row of rotor blades can thus be adjusted and, in particular also, balanced independently of the rotor blades of the next row of rotor blades. Moreover, if the heat shield elements are aligned at incorrect angles there are only slight deviations in the gap dimensions between the heat shield element and the guide vanes thanks to the small length dimensions of the heat shield elements. The gap between the heat shield elements and the guide vanes, which is to be designed in such a way that no rubbing of the guide vanes against the heat shield elements occurs, can consequently be made smaller. The heat shield elements in accordance with the second aspect of the invention are preferably also produced from a highly heat-resistant material, expediently with a low thermal conductivity.
The preferred embodiments of the invention presented below are based both on the first and on the second aspect of the invention.
In a preferred embodiment of the invention, the heat shield element is designed as a closed circular ring. In this arrangement, the rotor blades are preferably arranged on the circular ring. The self-contained circular ring completely surrounds the basic rotor element. A heat shield element embodied as a closed circular ring furthermore offers the advantage of a very small number of components. The circular ring can be preassembled with the rotor blades arranged on the circular ring before being arranged on the basic rotor element in a final assembly operation. The embodiment of the heat shield element as a circular ring furthermore results in the advantage of uniform distribution of mass on the circumference of the rotor. The uniformly distributed centrifugal forces caused by rotation lead to a self-centering concentric arrangement of the circular ring. On the basic rotor element. Moreover, temperature changes cause uniform radial expansion of the circular ring. It is a relatively simple matter here to match the thermal expansion of the components surrounding the rotor in the turbomachine, e.g. a casing, with the thermal expansion of the rotor.
As an alternative, the heat shield elements are expediently embodied as segments of a circular ring. The segments of the circular ring preferably extend over an angular range of 10 to 30 degrees. The segments lined up on the circumference of the basic rotor element form a self-contained circular ring surrounding the basic rotor element. The joints remaining between the individual segments are here made so small that only a small amount of working fluid flows into the joint. This only slight inflow of working fluid into a joint also leads to an only slightly increased thermal loading of the basic rotor element in the area of the basic rotor element adjoining the joint. Thanks to the segmentation of the circular ring, the heat shield elements can be mounted more easily on the basic rotor element. Moreover, reduced thermally induced stresses form in the heat shield elements in comparison with an embodiment of the heat shield element as a self-contained circular ring.
It is advantageous if the heat shield element or the heat shield elements has or have for the purpose of securing the rotor blades, at least one slot which extends essentially in the circumferential direction of the rotor and in which the rotor blades engage in a form-fitting manner by means of an engagement element in each case. The rotor blades are thus secured releasably on the heat shield element or heat shield elements. If, for example, individual rotor blades are damaged during operation, it is possible to renew just the damaged rotor blades in each case. It is also expediently possible for a plurality of slots extending essentially in the circumferential direction to be provided parallel to one another in the heat shield element or heat shield elements, by means of which a plurality of rows of rotor blades can be secured next to one another. However, it is equally possible, though implemented less often in practice for reasons connected with blade strength, to provide the slots in the rotor blades and the engagement elements on the heat shield elements. As an alternative to this, it is also possible, in another advantageous configuration, to embody the heat shield element or heat shield elements in one piece with the respective rotor blades arranged thereon. In this arrangement, the rotor blades are preferably produced as a casting together with the respective heat shield element. However, they can also be produced by machining. The one-piece embodiment on the one hand reduces the number of components and, on the other hand, significantly reduces the outlay on assembly. Moreover, there is no longer any need for complex design measures for securing the blades, as a result of which production costs are reduced. The heat shield element or heat shield elements is/are preferably in each case secured on the basic rotor element by means of one or more slots extending essentially in the axial direction and by means of engagement elements engaging in a form-fitting manner in these slots. Here, it is possible either for the slots to be made in the basic rotor element and the engagement elements on the heat shield elements or, conversely, to have the engagement elements on the basic rotor element and the slots in the heat shield elements. The heat shield elements can thus be pushed onto the basic rotor element and can also be dismantled again in the event of damage.
If a plurality of heat shield elements is lined up on the circumference of the basic rotor element or in the axial longitudinal direction of the basic rotor element, there is generally a joint remaining in each case between the heat shield elements, in particular for compensating for thermal expansion of the heat shield elements. It is expedient if the joint is sealed with a seal, preventing the working fluid from entering the joint. For this purpose, a seal, e.g. stuffing-type packing, a cord packing or a laminar strip seal, is preferably placed in slots in the form of slits which are arranged in the side walls of the joint. Such sealing of joints between heat shield elements is advantageous especially if, in a preferred embodiment of the invention, a flow of cooling fluid is passed through the intermediate gap or a plurality of intermediate gaps between the basic rotor element and the heat shield element or heat shield elements. For this purpose, the intermediate gap has a cooling-fluid inlet and a cooling-fluid outflow passage or an outlet opening which opens into the flow of the working fluid, for example. It is particularly expedient to make the intermediate gap between the heat shield element and the basic rotor element as continuous as possible. Here, the flow of cooling fluid serves, in particular, to cool the heat shield element or heat shield elements on their respective rear sides, which face the basic rotor element. Heat which penetrates a heat shield element is thus passed into the flow of cooling fluid and consequently does not pass into the basic rotor element.